In the discussion of ash plugging of a diesel particulate filter, which statements are correct?

• A. Oil incompatible with DPF
• B. Engine worn out and using too much oil
• C. Both A and B
• D. Neither A nor B

Answer: (C)

Ash plugging of a diesel particulate filter happens because non-combustible ash from lubricant additives ends up in the filter. The DPF is good at trapping soot and burning it off during regeneration, but ash from engine oil doesn’t burn away, so it gradually fills the filter. If the oil used isn’t designed for use with a DPF—i.e., it has higher ash content or additives that produce more ash—that extra ash accelerates plugging. At the same time, a worn engine that consumes more oil sends more oil into the combustion cycle, increasing the amount of oil-derived ash in the exhaust. So both using oil not compatible with the DPF and excessive oil consumption from a worn engine are real, contributing factors to ash buildup, making both statements correct.